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cid2spf.py
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cid2spf.py
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#!/usr/bin/python2.4
# Convert a MS Caller-ID entry (XML) to a SPF entry
# This should be obsolete now. It is included for historical interest.
#
# (c) 2004 by Ernesto Baschny
# (c) 2004 Python version by Stuart Gathman
#
# Date: 2004-02-25
# Version: 1.0
#
# Usage:
# ./cid2spf.pl "<ep xmlns='http://ms.net/1'>...</ep>"
#
# Note that the 'include' directives will also have to be checked and
# "translated". Future versions of this script might be able to get a
# domain name as an argument and "crawl" the DNS for the necessary
# information.
#
# A complete reverse translation (SPF -> CID) might be impossible, since
# there are no way to handle:
# - PTR and EXISTS mechanism
# - MX mechanism with an different domain as argument
# - macros
#
# References:
# http://www.microsoft.com/mscorp/twc/privacy/spam_callerid.mspx
# http://spf.pobox.com/
#
# Known bugs:
# - Currently it won't handle the exclusions provided in the A and R
# tags (prefix '!'). They will show up "as-is" in the SPF record
# - I really haven't read the MS-CID specs in-depth, so there are probably
# other bugs too :)
#
# Ernesto Baschny <[email protected]>
#
from __future__ import print_function
import xml.sax
import spf
# -------------------------------------------------------------------------
class CIDParser(xml.sax.ContentHandler):
"Convert a MS Caller-ID entry (XML) to a SPF entry"
def __init__(self,q=None):
self.spf = []
self.action = '-all'
self.has_servers = None
self.spf_entry = None
if q:
self.spf_query = q
else:
self.spf_query = spf.query(i='127.0.0.1', s='localhost', h='unknown')
def startElement(self,tag,attr):
if tag == 'm':
if self.has_servers != None and not self.has_servers:
raise ValueError(
"Declared <noMailServers\> and later <m>, this CID entry is not valid."
)
self.has_servers = True
elif tag == 'noMailServers':
if self.has_servers:
raise ValueError(
"Declared <m> and later <noMailServers\>, this CID entry is not valid."
)
self.has_servers = False
elif tag == 'ep':
if attr.has_key('testing') and attr.getValue('testing') == 'true':
# A CID with 'testing' found:
# From the MS-specs:
# "Documents in which such attribute is present with a true
# value SHOULD be entirely ignored (one should act as if the
# document were absent)"
# From the SPF-specs:
# "Neutral (?): The SPF client MUST proceed as if a domain did
# not publish SPF data."
# So we set SPF action to "neutral":
self.action = '?all'
elif tag == 'mx':
# The empty MX-tag, same as SPF's MX-mechanism
self.spf.append('mx')
self.tag = tag
def characters(self,text):
tag = self.tag
# Remove starting and trailing spaces from text:
text = text.strip()
if tag == 'a' or tag == 'r':
# The A and R tags from MS-CID are both handled by the
# ipv4/6-mechanisms from SPF:
if text.find(':') < 0:
mechanism = 'ip4'
else:
mechanism = 'ip6'
self.spf.append(mechanism + ':' + text)
elif tag == 'indirect':
# MS-CID's indirect is "sort of" the include from SPF:
# Not really true, because the <indirect> tag from MS-CID also
# provides a fallback in case the included domain doesn't provide
# _ep-records: The inbound MX-servers of the included domains
# are added to the list of allowed outgoing mailservers for the
# domain that declared the _ep-record with the <indirect> tag.
# In SPF you would use the 'mx:domain' to handle this, but this
# wouldn't depend on referred domain having or not SPF-records.
cid_xml = self.cid_txt(text)
if cid_xml:
p = CIDParser()
xml.sax.parseString(cid_xml,p)
if p.has_servers != False:
self.spf += p.spf
else:
self.spf.append('mx:' + text)
def cid_txt(self,domain):
q = self.spf_query
domain='_ep.' + domain
a = q.dns_txt(domain)
if not a: return None
if a[0].lower().startswith('<ep ') and a[-1].lower().endswith('</ep>'):
return ''.join(a)
return None
def endElement(self,tag):
if tag == 'ep':
# This is the end... assemble what we've got
spf_entry = ['v=spf1']
if self.has_servers != False:
spf_entry += self.spf
spf_entry.append(self.action)
self.spf_entry = ' '.join(spf_entry)
def spf_txt(self,cid_xml):
if not cid_xml.startswith('<'):
cid_xml = self.cid_txt(cid_xml)
if not cid_xml: return None
# Parse the beast. Any XML-problem will be reported by xlm.sax
self.spf_entry = None
xml.sax.parseString(cid_xml,self)
return self.spf_entry
if __name__ == '__main__':
import sys
if len(sys.argv) < 2:
print("""Usage: %s "<ep xmlns='http://ms.net/1'>...</ep>" """ % sys.argv[0], file=sys.stderr)
sys.exit(1)
cid_xml = sys.argv[1]
p = CIDParser()
print(p.spf_txt(cid_xml))